This invention relates to an alcohol content detector device for determining the nature of the fuel supplied to a burner or the like in a non-contact manner and, more particularly, to an alcohol content detector device for measuring alcohol content of the alcohol-containing fuel used in an engine for automobiles or the like.
Recently, the U.S.A. and various European countries have adopted, as an automobile fuel, a mixed fuel containing alcohol in gasoline for the purpose of reducing consumption of petroleum, and such fuel is being diffused gradually among consumers. However, when such alcohol-mixed fuel is used, as its is, in those combustion engines originally matched with the air-fuel ratio of the fuel gasoline, there occurs a leaning phenomenon due to the fact that alcohol has a smaller theoretical air-fuel ratio than that of gasoline, and other facts. On account of this, it becomes necessary to regulate the air-fuel ratio, the ignition timing of the engine, and so forth in accordance with the alcoholic content in the fuel by controlling an actuator such as fuel injection valve, etc. through detection of the alcoholic content in the alcohol-mixed fuel. The description of such conventional alcoholic content detector device will now be made in conjunction with the drawings.
FIG. 6 is a schematic diagram illustrating an engine control system having incorporated therein a conventional alcoholic content detector device. In the Figure, A designates an alcohol content detector, (20) is an engine, (21) is a fuel tank, (22) is a fuel pump disposed within the fuel tank (21), (23) is a fuel supply pipe connected to the fuel pump (22), (24) is a high pressure filter inserted in the fuel supply pipe (23), (25) is a fuel distributor connected to the fuel supply pipe (23), (26) is a fuel pressure regulator connected to the fuel distributor (26), (27), is a fuel injection valve connected to the fuel distributor (25), (28) is a fuel return pipe connected to the fuel pressure regulator (26), (29) is an intake pressure sensor connected to an air intake pipe (30), (31) is an air-to-fuel ratio sensor mounted to an exhaust pipe (32), (33) is an engine revolution sensor, (34) is an ignition plug mounted to the engine (34), and (35) is an engine control unit, to which various signals such as the signal from the alcohol content detector A, the signal from the intake pressure sensor (29), the signal from the air-to-fuel ratio sensor (31) and the signal from the engine revolution sensor (33) are inputted and which controls the fuel injection valve (27) and the ignition plug (34) at control amounts in accordance with the input. In the figure, when fresh fuel is supplied to the fuel tank (21), the mixed fuel mixed within the fuel tank (21) is pumped through the fuel supply pipe (23) and the high pressure filter (24) by the fuel pump (22) as soon as the engine (20) is started to be introduced to the alcohol content detector A, where the alcohol content is measured. The fuel then flows into the fuel distributor (25) from where one portion of the fuel is supplied to the engine (20) through the fuel injection valve (27), and the other portion of the fuel is returned to the fuel pump (21) through the fuel pressure regulator (26) and the fuel return pipe (28). The fuel then flows into the fuel distributor pipe (25) and one portion thereof is supplied to the engine (20) through the fuel injection valve (27) and the remaining portion is returned to the fuel tank (21) through the fuel pressure regulator (26) functions to maintain the fuel pressure in the pipe up to the fuel pressure regulator (26) constant irrespective of the amount of injected fuel. When the alcohol content measured in the alcohol content detector A is inputted into the engine control unit (35), the engine control unit (35) determines the engine conditions on the basis of the signals from the engine rotation sensor (33) and the air intake pressure sensor (29) to control the valve-open time of the fuel injection valve (27), thereby changing the fuel amount supplied to the engine (20), and the air-to-fuel ratio is detected by the air-to-fuel ratio sensor (31) so that it is feed-back controlled toward a target value corresponding to the above engine conditions, upon which the ignition timing of the ignition plug (34) is controlled in accordance with the engine conditions.
FIG. 7 is a schematic diagram illustrating a conventional alcohol content detector, in which (1) is a light emitting element, (2) is a diaphragm disposed in front of the light emitting element (1), (3) is a collecting lens disposed in front of the diaphragm (2), (4) is a collected light beam and (5) is a cylindrical transparent body having formed thereon a refraction surface (51) which is cut at a predetermined angle relative to its longitudinal axis and which is in contact with the fuel introduced from the fuel inlet (81), (6) is a back side reflection mirror having a reflection surface on the opposite side of the fuel-contacting surface, (7) is a first dimension position detector element, which in this example is a semiconductor position detector element (hereinafter referred to as PSD), (8) is a case having formed therein the fuel inlet (81) for introducing the fuel onto the refraction surface (51) of the cylindrical transparent body (5), (9) is a seal including a seal portion (91) which seals between the cylindrical transparent body (5) and the case (8) and a seal portion (92) which seals between the case (8) and the fuel passage, (10) is a detection circuit comprising a current-voltage converter (101) for the photocurrent from the PSD (7), an adder (102), a divider (103), an output gain setting portion (104), an output bias setting portion (105) and a driver (106) for driving the light emitting element (1).
In the figure, when the light emitting element (1) disposed at one end of the cylindrical transparent body (5) is driven by the driver (106) to emit light, the emitted light passes through the diaphragm (2) and collected by the collective lens (3). The collected light beam (4) impinges at an incident angle .phi. at a point Po on the fuel-contacting refraction surface (51) disposed at the other end of the cylindrical transparent body (5) to refract at the refraction surface (51) at a refraction angle X determined in accordance with the difference between the index of refraction Nf of the fuel and the index of refraction Nd of the cylindrical transparent body (5) EQU X=arcsin (Nd/Nf.times.sin.phi.).
The refracted light passes through the fuel and reflected at the reflection surface P1 on the back side reflection mirror (6) to again pass through the fuel and impinges again at a point P2 on the refraction surface (51), where the light refracts in accordance with the above equation between the incident angle .phi. and the refraction angle X to pass into the cylindrical transparent body (5) and reach the PSD (7) disposed on the same side of the light emitting element (1). The collection lens (3) is adjusted so that the collected light beam (4) is focused substantially on the PSD (7). When the collected light beam (4) impinges on the PSD (7), photo-currents ir1 and ir2 corresponding to the incoming light amount flow from the PSD (7) to each of electrodes I1 and I2, the photo-currents ir1 and ir2 being divided in inverse proportion to the distance to the electrodes. That is, the distance X from the electrode I2 of the PSD (7) to the light impinging position is expressed by EQU X=L.times.ir1/ (ir1+ri2)
where L is the distance between the electrodes. At this time, the distance X coincides with the center of gravity of the spot of the impinged light beam. Each of the photo-currents ir1 and ir2 is inputted to the detector circuit (10) and current-voltage converted into Vr1 and Vr2, respectively, in the current-voltage conversion unit (101). The voltages Vr1 and Vr2 are added in the adder (102) and the divider (104) computes Vr1 / (Vr1+Vr2) on the basis of the voltage Vr1 and the result of the above addition. The computation result is multiplied by an output voltage gain K in the output gain setting unit (103), and a predetermined voltage bias Vo is applied at the output bias setting unit (105), whereby a voltage Vout corresponding to alcohol content Cm given by the equation Vout=K.times.vr1 / (vr1+Vr2)+Vo is outputted. FIG. 8 is a graph illustrating the output characteristics of the alcohol content detector in connection with a methanol-gasoline mixed fuel, from which it is seen that, when the alcohol content is 0%, i.e., pure gasoline only, the difference in refraction index between the gasoline and the cylindrical transparent body (5) is small, so that the collected light beam (4) impinges on the PSD (7) on the side close to the light emitting element (1) to establish the relationship ir1&lt;ir2, and when the alcohol content is 100%, i.e., pure methanol only, the difference in refraction index between the gasoline and the cylindrical transparent body (5) is large, so that the collected light beam (4) impinges on the PSD (7) on the side remote from the light emitting element (1) to establish the relationship ir&gt;ir2, whereby the illustrated output characteristic is obtained.
When the engine (20) stops at an elevated temperature and the fuel pump (22) stops, the fuel pressure in the high pressure pipe decreases and bubbles generate within the pipe, establishing a state in which bubbles exist within the fuel at the time of re-starting the engine, and when the alcohol content detector is connected in the fuel return pipe (28) at the downstream of the fuel pressure regulator (26), the fuel containing bubbles generated by the cavitation phenomenon at the fuel pressure regulator (26) passes through the alcohol content detector. However, in the conventional alcohol content detector, the bubbles mixed within the fuel cannot be detected even when they passed through the detection unit of the detector and the output change due to the passage of the the bubbles is erroneously recognized as the change in alcohol content. FIG. 9 is a sectional view of the detection unit of the conventional alcohol content detector, which illustrates the state in which the bubbles (36) in the fuel introduced from the fuel inlet (81) are in the vicinity of the refraction surface (51) of the cylindrical transparent body (5). In this condition, since the difference in the index of refraction of the cylindrical transparent body (5) and the index of refraction of the bubbles (36) is large, the collected light beam (4) passing through the cylindrical transparent body (5) is refracted at a large angle at the refraction surface (51) and is scattered or absorbed at the casing (8) and the like, so that only a very weak scattered light or no light at all impinges at the PSD (7), causing the output Vout to exhibit an unstable value which does not depend upon the alcohol content. That is, in the conventional alcohol content detector, the output variation due to the bubbles and the output alcohol cannot be distinguished from each other, so that change in output due to the bubbles is erroneously recognized as the output change due to the change in alcohol content and the engine fuel amount, the ignition timing and the like are controlled. Therefore, there was a fear that a mulfunction of the engine such as non-smooth starting of the engine and an abrupt engine stall may occur depending upon the conditions of the bubbles.